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We present a study of dust acoustic shock waves in a non-Maxwellian plasma with dust charge fluctuations, which are seen to cause a dissipation term in fluid model, and consequently shocks are generated. In particular, we focus on dust acoustic waves as affected by various dust size distributions. Two distinct dust size distributions—the polynomial and the power law distributions—have been used. For analytical investigation of nonlinear wave propagation in complex plasmas, a reductive perturbation approach is used to obtain the Burgers equation. A dusty plasma system with non-Maxwellian Kappa distribution is considered and it is shown that the amplitude of a shock wave, for the dust size distribution is larger than that for the mono-sized counterpart, while the shock width manifests an opposite trend. Furthermore, the shock wave speed is also affected by the dust size distributions as well as by the nature of velocity distribution function. To benchmark our findings, we apply the proper limit on the spectral index, i.e., κ → ∞ , and retrieve the Maxwellian results. The current findings are crucial for comprehending respective shock distributions for a plasma system exhibiting non-thermal characteristics and having dust size distributions. [ABSTRACT FROM AUTHOR]

Solitary waves in a symmetric pair-ion plasma are studied as affected by various plasma parameters, e.g., electron density, collision frequency, ion temperatures, (r, q)-distributed electrons. In this regard, plasma fluid equations have been used to simulate the plasma system for which a reductive perturbation technique is applied to derive the relevant damped Korteweg–de Vries equation. The effects of spectral indices, collision frequency, ion-electron temperature ratios, and density on the time evolution of perturbed potential profile have been illustrated and benchmarked with Boltzmann distributed electrons. It is observed that the nonthermal population significantly affects the soliton amplitude, which increases with r and q. Furthermore, it also grows with electron density and ion temperature; however, there is a in the slowing down rate in the case of the latter. An increase in the collision frequency leads to faster damping in both the amplitude and speed of the solitary potential profiles. This work will be useful in the determination of plasma dynamics for pair-ion plasma systems containing nonthermal electrons, especially with flat-topped distribution functions, e.g., as found in Earth's magnetosheath and magnetotail, as well as in laboratory experiments with the fullerene plasma. To the best of our knowledge, a general description for pair ion plasmas using (r, q) distribution has never been reported. This study can explore a huge variety of velocity distribution functions—via the two index nonthermal parameters, in contrast to single index counterparts. [ABSTRACT FROM AUTHOR]

Experimental and numerical approaches have their own advantages and limitations, in particular, when dealing with complex phenomena such as snow particles falling at moderate Reynolds numbers (Re). Time-resolved, three-dimensional particle tracking velocimetry (4D-PTV) experiments of free-falling, three-dimensional (3D)-printed snowflakes' analogs shed light on the elaborate falling dynamics of irregular snow particles but present a lower resolution (tracer seeding density) and a limited field of view (domain size) to fully capture the wake flow. Delayed-detached eddy simulations of fixed snow particles do not realistically represent all the physics of a falling ice particle, especially for cases with unsteady falling attitudes, but accurately predict the drag coefficient and capture the wake characteristics for steadily falling snowflakes. In this work, we compare both approaches on time- and space-averaged flow quantities in the snowflake wake. First, we cross validate the two approaches for low Re cases, where close agreement of the wake features is expected, and second, we assess how strongly the unsteady falling motion perturbs the average wake pattern as compared to a fixed particle at higher Re. For steadily falling snowflakes, the fixed-particle model can properly represent the wake flow with errors within the experimental uncertainty (±15%). At moderate/high Re (unsteady falling motion), larger differences are present. Applying a co-moving frame to the experimental data to account for the particle movement or filtering the numerical data on larger grids reduces these differences only to some extent, implying that an unsteady fall significantly alters the average wake structure as compared to a fixed particle model. [ABSTRACT FROM AUTHOR]

This paper has proposed a parameter estimation method for a laser welding process inherently highly nonlinear as a result of the highly nonlinear inputs and outputs of the system. Hence, a nonlinear system identification method was developed for the laser welding process using the wavelet network nonlinear autoregressive exogenous (ARX) model. The advantage of ARX over the standard nonlinear models is that it not only considers the delayed input and output regressors but also uses nonlinear functions for mapping, thus making ARX a better candidate for the prediction of nonlinear behaviors. In total, nine available datasets for the training and test phases at pulse durations, pulse frequencies, focal lengths, currents, and welding speeds were considered. Five inputs including pulse duration, pulse frequency, focal length, current and welding speed, and temperature as one output were considered. The first eight datasets were utilized for the training phase and one was used for the testing phase. The results showed that the ARX model had an acceptable performance in training and test phases, and it was capable of identifying the nonlinear and time-variant phenomenon of the laser welding process examined in this paper. For instance, most fitness values for austenitic and ferritic steel samples in the training time histories were 97.13 and 97.95, respectively. [ABSTRACT FROM AUTHOR]

Electron temperature gradient (ETG) driven solitons are investigated having gradients in equilibrium electron temperature and equilibrium number density and with electron shear flow. In a linear regime, using model equations, a linear dispersion relation has been analysed analytically as well as numerically. ηe and electron to ion temperature ratio effects, real frequency, and growth rate of ETG instability are determined. In the nonlinear regime, the Korteweg--de Vries equation for the ETG mode has been derived and analysed numerically which shows that it admits solitary wave solutions. It can also be noted that soliton amplitude is sensitive to ηe, the magnetic field, and the temperature ratio. This work may be helpful for low frequency electrostatic modes in nonuniform electron-ion plasma having gradients in density and electron temperature and also in tokamak plasma. [ABSTRACT FROM AUTHOR]

Linear and nonlinear properties of electrostatic waves on the ion time scale in a collisional rotating magnetoplasma with warm relativistically streaming ions and non-Maxwellian electrons have been investigated here. In the weak nonlinearity limit, we have derived Zakharov-Kuznetsov-Burgers equation to study the shock wave propagation in dissipative magneto-rotating plasmas with non-Maxwellian electrons. It has been found that ion acoustic shock waves with kappa distributed electrons admit only compressive shock structures, however, the ones with Cairns distributed electrons have been shown to allow for the formation of both compressive and rarefactive structures. This change in behavior has been found to be closely linked with the difference in the shapes of both distribution functions. The dependence of the characteristics of ion acoustic shock structures on rotation, obliqueness, relativistic streaming, kinematic viscosity and non-Maxwellian electrons has also been explored in detail. The relevance of the work with regard to planetary magnetospheres and pulsars has also been pointed out. [ABSTRACT FROM AUTHOR]

Nonlinear structure formation in ion-temperature-gradient (ITG) driven waves is investigated in pair-ion plasma comprising ions and nonthermal electrons (kappa, Cairns). By using the transport equations of the Braginskii model, a new set of nonlinear equations are derived. A linear dispersion relation is obtained and discussed analytically as well as numerically. It is shown that the nonthermal population of electrons affects both the linear and nonlinear characteristics of the ITG mode in pair-ion plasma. This work will be useful in tokamaks and stellarators where non-Maxwellian population of electrons may exist due to resonant frequency heating, electron cyclotron heating, runaway electrons, etc. [ABSTRACT FROM AUTHOR]